OK, time for a decision. You have two options.

1. You can run a HiC2 pool (chlorine above 10 ppm, dosing 1x per week, etc) AND you can work on lowering your calcium by adding soda ash slowly upstream of your filter. Each time you do this, you will collect some calcium carbonate on the filter, but some more will cloud the pool. You'll have to turn the pump off for 12 - 24 hours to let the calcium settle, then vacuum it up and clean your filter. I'm not sure how much calcium you'll be able to remove on each pass.

OR

2. You can drain most of your pool and refill. To reach CYA = 80 ppm, you'll need to drain 2/3 of the pool. This will also lower your calcium hardness to around 230 ppm. This would be easiest; but whether it's best depends on your preference and how much water costs there. Obviously, the first option will be cheapest, even when you allow for spending $100 on soda ash, acid, and extra DE.